The present invention relates generally to a table saw fixture and particularly to a fixture and fixture combinations which provide accurate alignment to enable square cuts to be made on a workpiece. The invention also relates to a method of verifying the alignment of the arbor for the cutting blade, relative to the guide groove in the work supporting table of a table saw, as well as a method of and apparatus for adjusting the alignment of the arbor relative to the guide groove.
The modern table saw has a work supporting table which is provided with a slot and at least one guide groove in the upper surface of the table which is parallel with the slot. A circular cutting blade is mounted on an arbor which is rotatably mounted on a cradle which is connected to the table so that the blade extends through the slot in the table. The cradle is mounted on the table so that it can be raised or lowered and so that it can be rotated about a front to back horizontal axis. This enables the operator to adjust the amount of cutting height of the saw and the cutting angle of the saw, relative to the upper surface of the work supporting table.
The arbor supporting cradle in most modern table saws is pivotally mounted between a pair of trunnions. One trunnion is fastened to the bottom surface of the supporting table at the front end of the table saw. The other trunnion is fastened to the bottom surface of the supporting table at the rear end of the saw. The rear trunnion is fastened by bolts which extend through oversize holes in the rear trunnion. This enables the rear trunnion to be moved laterally a small amount, relative to the front trunnion, to correct for a possible misalignment of the arbor relative to the guide groove in the work supporting table. It is essential that the arbor be at a right angle to the guide groove so that the cutting blade is parallel with the guide groove of the supporting table. If the cutting blade is not parallel with the guide groove, the bolts which fasten the rear trunnion to the supporting table are loosened and the rear trunnion is forced into an adjusted position, for example by striking the trunnion with a hammer to move the rear trunnion laterally and to change the alignment of the cutting blade relative to the guide groove. This represents a crude and imprecise adjusting feature. It is extremely difficult to align the cutting blade relative to the guide groove with any degree of accuracy by the use of hammer blows. Also, even if an accurate alignment of the cutting blade is achieved, the achieved correct alignment can be lost when the bolts which hold the rear trunnion to the table are tightened.
The accurate cutting of a workpiece can be affected by factors other than the alignment of the cutting blade to the guide groove of the supporting table. These other factors include a cutting blade which may not be perfectly flat, an arbor which may not be perfectly straight and a guide groove which does not have a uniform width or is too wide for the guide bar of a fixture which is used for a cutting operation.
Verification devices have been developed for checking the alignment of the cutting blade with the guide groove of a table saw and for the flatness of the cutting blade. A typical verification device includes an elogated guide bar for slidable mouting in the guide slot of the work supporting table, a cross bar which is connected to the guide bar for supporting a gauge such as a feeler gauge which has a dial face, a dial and a plunger which is mounted of the gauge for axial movement relative to dial face and which is operatively connected to the dial. Although the gauge portion of the verification device is a very accurate instrument, inaccurate readings are obtained from the gauge due to a less than precise fit of the guide bar portion of the verification device within the guide groove and the lack uniformity in the width of the groove. One prior art specification device utilizes a split bar which can be adjusted to fit into the guide slot by screws which are threaded into the bar. However, the device must be readjusted for another application. Also, prior art verification device which employ a dial gauge are limited in the ways that they can be used, due to the manner in which the dial gauge is mounted on the cross bar.
Inaccurate cutting of a workpiece occurs even if the longitudinal axis of the arbor is properly aligned with the guide groove and the guide bar of the fixture, such as a miter gauge, fits perfectly in a perfectly uniform guide groove. Inaccurate cuttings can occur if the arbor is not straight or if the cutting blade is not flat. If the arbor is straight and the guide bar of the fixture fits perfectly in the guide groove of the table saw, a misalignment of the arbor relative to the guide groove or a warp in the cutting blade can be detected by existing verification devices. However, there is no effective way to determine the straightness of the arbor without removing the arbor from the table saw or of making a proper adjustment of the arbor if one or more other variables which affect alignment are present. If there are errors or flaws in two or more variables, it is very difficult to verify and isolate the flaws and to correct them.
Proper alignment of the cutting blade and fixtures is particularly critical when the table saw is used for cutting very thin strips from a workpiece, i.e. for cutting veneer strips. For such thin pieces, uniformity of thickness is critical. Cutting accuracy must be maintained with low tolerance for error. Also, there is a lower limit to the width of strip which can be cut on a table saw by using conventional equipment and methods. Still further, precise cuts are extremely difficult to obtain on a conventional table saw, using conventional fixtures. These and other difficulties experienced with the prior art table saws, table saw fixtures, and method of using the fixtures with table saws have been obviated by the present invention.
It is, therefore, a principal object of the invention to provide a verification apparatus for checking all variables in a conventional table saw which contribute to alignment errors between the cutting blade and guide groove in the work supporting table of the table saw.
Another object of the invention is the provision of a method of checking and measuring all variables in a conventional table saw which contribute to alignment errors between the cutting blade and the guide groove in the work supporting table of the table saw.
A further object of the invention is the provision of an apparatus for and a method of positively and precisely aligning the arbor of a table saw relative to the guide groove in the work supporting table of the table saw.
It is another object of the invention to provide a self-adjusting guide bar for sliding in the guide groove of a table saw for use with a plurality of saw fixtures and which maintains a constant and precise relationship between the fixture and the cutting blade of the table saw.
A still further object of the invention is the provision of an alignment gauge which has improved precision and versatility.
It is a further object of the invention to provide a locating gauge for use in a table saw to enable narrow pieces to be cut from a workpiece with improved accuracy and uniformity.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts and steps set forth in the specification and covered by the claims appended hereto.
The present invention includes an accessory for a table saw which has a fixture which is connected to a self-adjusting guide mechanism for sliding in the guide groove in the upper surface of the work supporting table of a table saw. The guide mechanism includes an elongated bar for sliding in the guide groove and at least two spaced yieldable compensators which protrude from one vertical side surface of the bar for engaging one of the side surfaces of the guide groove of the supporting table to maintain the opposite vertical side surface at the bar snugly against the opposite side surface of the guide groove. More specifically, each compensator includes a horizontal bore in the guide bar, a plunger for extending beyond one of the vertical side surfaces of the bar, a stop for limiting the amount by which the compensators protrude beyond the side surface of the bar, and means for biasing the plunger against the stop. In one form of the invention, the fixture is a miter gauge. In a second form of the invention, the fixture is an alignment gauge. In a still further form of the invention, the fixture is a work locating gauge for cutting narrow strips from a workpiece. The present invention also includes a method of verifying the straightness of the arbor on which the cutting blade is mounted in the axial alignment of the arbor relative to the guide groove of the table saw. The straightness of the arbor in a table saw is preferably verified by applying a reference plate which has a flat reference surface and a bore which is transverse to the reference surface onto the arbor of a table saw so that the reference plate rests against the conventional cutting blade locating stop of the arbor and the reference surface of the reference plate faces the guide groove of the table saw. The straightness of the arbor can be checked by a saw blade which is not necessarily perfectly flat as long as the saw blade remains stationary. An alignment gauge is applied to the guide groove of the table saw. The alignment gauge has an elongated guide bar for sliding in the guide groove and a cross bar which supports a dial gauge and a feeler rod which is slidingly mounted relative to the dial gauge for movement toward and away from the reference surface of the reference plate. The alignment gauge is positioned so that the feeler rod engages the surface of a reference plate and the arbor is rotated to a plurality of angular positions relative to the reference plate while maintaining the reference plate in a fixed position so that gauge readings can be taken at each of the angular positions. The right angle alignment of the arbor can be verified by applying the reference plate to the arbor so the plate extends through the slot for the cutting blade in the work supporting table and above the upper surface of the table. The alignment gauge is applied to the saw so that the guide bar of the gauge is slidably mounted in the guide groove and the feeler rod of the dial gauge extends to the reference surface of the reference plate. The alignment gauge is positioned at a first point in the guide groove of the work supporting table so that the feeler rod engages a first point at the front of the reference surface of the reference plate to obtain a first gauge reading. The dial gauge is then positioned at a second point along the guide groove of the work supporting table saw so that the feeler rod engages a second point at the rear of the reference surface of the reference plate to obtain a second gauge reading. The first and second readings are compared to determine if the arbor is at a right angle to the guide groove. In addition to the reference plate, the apparatus for verifying the straightness of the arbor in a table saw also includes a cap which is fixed to the free end of the arbor and a compression spring for mounting on the arbor between the reference plate and the cap to bias the reference plate against the stop on the arbor. This enables the arbor to be rotated relative to the reference plate and stopped at periodic increments of rotation so that a gauge reading can be taken each time that the arbor stopped.
The present invention also includes a method of and an apparatus for changing the alignment of the arbor if it is determined by the verification apparatus and method that the arbor of the present invention is not at a right angle to the guide groove of the supporting table. The alignment apparatus and method of the present invention are applicable to table saws in which the arbor is supported for rotation on a cradle which is, in turn, pivotally mounted between a pair of trunnions wherein each trunnion has a pair of flanges which enable the trunnion to be connected to the work supporting table by a pair of bolts. Each flange has a vertical aperture which is vertically aligned with a threaded vertical aperture in the work supporting table. The alignment apparatus of the present invention includes a pair of L-shaped brackets having a vertical leg and a horizontal leg. The vertical leg has a threaded aperture for receiving an adjusting screw. The horizontal leg has a vertical hole for receiving a bolt. Realignment of the arbor is accomplished by removing the bolts, one at a time, which connect one of the trunnions to the work supporting table of the table saw and positioning the brackets at opposite sides of the trunnion so that the horizontal leg portions of the brackets are below the flanges of the trunnion and the hole in the horizontal leg of each bracket is vertically aligned with the aperture in the flange with which the horizontal leg is engaged. A bolt is extended through the hole in the horizontal leg portion of each bracket and the aperture of the corresponding flange of the trunnion. The bolts are threaded into the threaded apertures in the table to support the L-shaped brackets and the trunnion but not tightened so that the trunnion is loosely connected to the supporting table and the trunnion is free to be moved laterally a slight amount. The trunnion is moved laterally to change the alignment of the arbor by rotating one of the adjusting screws until it engages the end edge of the flange. Additional rotation of the adjusting screw causes the trunnion to move laterally toward the other L-shaped bracket until the arbor is at a right angle to the guide groove of the table saw as verified by the verification apparatus of the present invention. The other adjusting screw is then advanced until it touches the edge of the opposite flange of the trunnion so that the trunnion is essentially locked in its correct position with respect to the right angle alignment of the arbor with the guide groove of the work supporting table. Each adjusting screw is provided with a lock nut to make sure that the trunnion remains in the correct set position. The trunnion bolts can then be tightened to secure the trunnion in the correct adjusted position.